Field of the Disclosure
The present disclosure relates to a piezoelectric sensor.
Description of the Related Art
A structure in which a piezoelectric layer is sandwiched between two electrode layers is known to be the structure of a general piezoelectric device used for sensors, actuators, and the like. In the piezoelectric device, physical signals, e.g., stress, applied to the piezoelectric device are converted to electric signals (direct piezoelectric effect) and are output from the electrodes, or electric signals input into the piezoelectric device are converted to physical signals (inverse piezoelectric effect).
In recent years, miniaturization and weight reduction of piezoelectric devices used for sensors and the like have been required in accordance with the miniaturization of electronic equipment. In order to address this requirement, development of a piezoelectric device in which a thin film piezoelectric layer is disposed on a film-shaped base material or a piezoelectric device composed of a film material having a piezoelectric property has been conducted.
Such a piezoelectric device has high impedance and is susceptible to noise. Therefore, for the purpose of eliminating electromagnetic noise and increasing sensitivity, enhancement of a shielding effect of the piezoelectric device has been proposed.
For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2006-253416) discloses a switching device (piezoelectric device) having a structure in which piezoelectric layers 3 and 3′ and substrates 2 and 2′ (insulating films) are stacked on both sides of an inner electrode layer 4 and are shielded by outer electrode layers 5 and 5′. In this regard, a hole (energization window) 6 is disposed in the outer electrode layer 5′ and the like, and signals are output from the inner electrode layer 4 (refer to FIGS. 2A and 2B and the like).
In addition, Patent Document 2 (Japanese Unexamined Patent Application Publication No. 8-75575) discloses a piezoelectric sensor having a structure in which electrodes 10 and 11 are disposed on both surfaces of a piezoelectric material 9 and are shielded by protective layers 12 and 13, shield layers 14 and 15, and insulating layers 16 and 17 in the form of a stacked structure.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-253416
Patent Document 2: Japanese Unexamined Patent Application Publication No. 8-75575